I guess this part is not required as by default the inbound access would be restricted for the above mentioned Network addresses and you don't need to deny by specifying it.

You're right its not necessary to explicitly deny these addresses as the explicit or implicit deny at the end of the ACL will drop those packets. It is, however, common practice to add those source networks at the beginning of an "external ACL". This allows the firewall to drop bogus source addresses (bogons) early in the ACL. This can speed things up if a more complex ACL is in use.

Also please refrain from using or advising others to use the conduit and outbound commands. While these commands are still available in the 6.x series they have been removed from 7.x. Please use access-lists in order to permit and deny access across interfaces.